Our aim is to analyze at the level of membrane and molecular mechanisms, how the spontaneous, coordinated, burst pattern of the crustacean cardiac ganglion (CG) is modulated by endogenous, well-characterized peptide and amine neurohormones, and how these are released from the pericardial organ (PO). The ganglion, together with its neurohormonal modulator, is regarded as a highly simplified, definable model system whose detailed study will yield insights about the mechanisms by which hormones act to modulate more complex behavior. The long-term goal is to understand the complete process: from control of the release of these neurohormones from the PO, to their effects on their target, the cardiac ganglion, to the expression of a well-defined behavior, the beating of the heart. An analysis of membrane activity in peptidergic and/or aminergic nerve terminals will alllow an understanding of stimulus-secretion coupling mechanisms. The ability to obtain single channel recordings and measure capacitance from in situ terminals in crustaceans will permit the study of Ca- and other channels in response to 'normal' activation. Different systems, PO vs X-organ vs CG, can be tested in order to discover if novel cation channels already found in sinus gland are unique to nerve terminals and what role they may play. By using specific agents, such as calmodulin and phosphoinositol inhibitors and C-kinase activators, we hope to probe hypothesized sequence of events underlying stimulus-secretion coupling. Voltage-clamping techniques on isolated somata and neuropil regions of the cardiac ganglion have been successfully used to characterize the kinetics and voltage dependence of the ionic currents underlying the rhythmic activity of the ganglion. The effects of each of the pericardial organ neruohormones on each of the analyzed currents will be assessed. These hormones include 5-hydroxytryptamine, octopamine, dopamine, acetylcholine and two peptides: proctolin and the trypsin-sensitive cardioexcitor.